The present invention relates in general to police radar detectors and, more particularly, to police radar detectors and methods of operating police radar detectors wherein selected operating frequencies permit a sweep of radar signals within the K and K.sub.a radar bands during one sweep of a local oscillator of a heterodyne receiver of the radar detector to produce intermediate frequency signals around 5 gigahertz (Ghz). The invention also resolves ambiguities which arise regarding the frequencies of detected police radar signals so that detection of radar signals within specific police radar bands are identified.
Police have used radar waves to monitor the speed of motor vehicles for many years. The frequencies currently licensed in the United States for police radar waves include: the X band--10.50 Ghz to 10.55 Ghz; the K band--24.05 Ghz to 24.25 Ghz; and, the K.sub.a band--33.40 Ghz to 36.00 Ghz. To alert motorists of the presence of police radar, electromagnetic signals within these police radar bands are monitored using a police radar detector which issues an audible and/or visual alert upon detection of a radar signal within one of bands.
Police radar detectors are basically superheterodyne radio receivers in which the tuning of the receivers is repeatedly swept through the frequencies which are to be received or detected, i.e., the frequencies of the licensed police radar bands. A typical superheterodyne radio receiver includes a mixer for receiving electromagnetic signals and a local oscillator (LO) signal to convert the frequency of the received signals to the frequency of an intermediate (IF) amplifier with the LO being swept in frequency to tune the required frequencies. Incoming electromagnetic signals can then be received at the LO frequency plus or minus the IF frequency. Generally, only one of these two signals, know as upper and lower sidebands, respectively, is to be received and the other or image frequency is suppressed by filtering or phasing to thereby perform single sideband (SSB) reception.
Frequencies used within a police radar detector, i.e., frequencies or swept frequency bands of local oscillators and frequencies of intermediate amplifiers, are referred to in the art as frequency schemes and a variety of frequency schemes are known and utilized in police radar detectors. For example, see U.S. Pat. Nos. 5,068,663; 5,268,689; and 5,305,007.
While known frequency schemes are satisfactory for operation of police radar detectors, there is an ongoing need for new and advantageous frequency schemes which improve operation of police radar detectors, reduce costs of manufacturing police radar detectors and/or simplify circuitry or operation of police radar detectors.